It is known to form seating spring assemblies by applying a plastic coating to a series of elongate sinuous spring wires which are positioned in adjacent relationship to each other with each of the wires touching each of its adjacent wires at frequent intervals along their lengths. For example, this type of seating spring assembly is disclosed in U.S. Pat. Nos. 3,843,477; 3,774,967; 3,767,261; 3,720,568; 3,709,559; and 2,803,293. As disclosed in these patents, the plastic coating is applied by dipping the spring wire assembly into the plastic coating material while the individual spring wires are held in aligned position with each of the wires touching each of its adjacent wires at frequent intervals along their lengths. The assembly is thereafter held together by the plastic coating without substantially restraining the flexing of the spring wires, and the coating itself provides a stretching and contracting spring action between adjacent wires, thereby giving a two-way stretch action to the spring assembly. This type of spring assembly is particularly useful in forming the seats and backs of chairs and the like.
The spring wires must be maintained in the proper touching relationship while the plastic coating is applied. If any location between adjacent wires is not maintained in the proper position, the plastic coating will not properly interconnect and resiliently hold the adjacent wires together at these locations. However, it is very difficult to hold the entire lengths of adjacent spring wires in the proper touching relationship during the plastic coating process with the result that a large number of the coated spring assemblies must be rejected.
Several different methods have been proposed for maintaining the spring wires in the proper relationship during the plastic coating process. For example, U.S. Pat. No. 3,843,477 discloses a hand-operated tool for holding the spring wires together (FIGS. 19-21) while the spring assembly is dipped into the coating material to apply the plastic coating thereto. This type of tool has been found to be effective in holding the opposite end portions of adjacent spring wires in the proper position but it is not very effective in holding and maintaining the medial portions of adjacent spring wires in the proper position so that a large number of the plastic coated spring assemblies must be rejected.
U.S. Pat. No. 2,803,293 discloses the use of metal clips or bands positioned at spaced apart touching locations along the spring wires and surrounding and holding together adjacent touching portions of adjacent wire springs. These metal clips or bands do hold the adjacent spring wires in the proper locations during application of the plastic coating but are expensive to apply and limit the normal flexing of the spring wires and the normal stretching and contracting of the plastic coating.
U.S. Pat. Nos. 3,720,568 and 3,774,967 (FIG. 29 of both patents) discloses applying a permanent metal weld to join together the opposite end portions of adjacent spring wires of the spring assembly. These permanent welds do maintain the opposite end portions of adjacent spring wires in the proper location; however, they do not maintain the medial portions of adjacent spring wires in the proper location during the plastic coating process. Also, these permanent welds tend to limit flexibility of the opposite edge portions of the spring assembly.